The general goals of the Histopathology Core are to provide high- quality pathology-related services to the investigators of the Program Project in an economical and timely manner. Two of the three projects will rely heavily on the Core's services. The main services they require include: (1) processing tissue samples to paraffin blocks; (2) sectioning blocks to slides; (3) staining slides with hematoxylin and eosin (H&E); and (4) immunostaining slides for several biomarkers. Processing tissue to paraffin blocks and H&E staining of slides are routine procedures essential for the microscopic evaluation of tissue samples, and will be relied on to identify and characterize proliferative breast lesions in the rodent models. Immunostaining will provide essential baseline biological information about the samples. The fours markers to be evaluated routinely include estrogen receptor, progesterone receptor, p53 protein expression, and cellular proliferation rate (by detecting cells incorporating BrdU during S-phase of the cell cycle). These assays rely on commercial polyclonal primary antibodies and enzyme-based detection systems and are established procedures in the laboratory. The Core will also support pilot studies to characterize potentially interesting new gene products identified during investigators' studies. This will primarily involve developing immunohistochemical assays and profiling expression in appropriate tissue samples. The Core, through collaboration with the new Breast Center at Baylor College of Medicine, will also have access to thousands of well-characterized human breast cancers to evaluate the clinical significance of especially promising factors identified in the animal studies. On a lesser scale, the Core will provide other services including staining whole mounts of mammary glands (approximately 150 samples/year) and pathology consultation for interpreting H&E stained and immunostained slides. Core personnel are experienced and qualified to provide all these services.